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Show The primary objective of this investigation was to determine the effects of various levels of air staging i.e. ratios of primary to secondary air on the sulphation of calcium oxide. In addition, the effects of temperature and fluidizing velocity were also assessed. it is hoped that these data will aid in optimising the best level of air-staging for combined NOx and SOx reduction. The experimental investigation covered the following (i) The acquisition of datum data under unstaged conditions with and without limestone for 'comparative purposes' in assessing subsequent SO retention under staged conditions. The operating conditions re' at i ng to these datum tests corresponded as near as poss i b 1 e to those currently used in shallow bed boilers i.e. an (as fired) excess air level of about 20-40%, a bed temperature of 850·C and a fluidizing (primary) air velocity of 1.5 m/s - 2.0 m/s. (ii) An evaluation of sulphur retention for various levels of air staging. Levels of air staging investigated were, 85:15, 70:30 and 60:40 equivalent to a primary air factor (PAF) of about 1.19, 0.95 and 0.84 respectively at 40% of total excess air. The PAF is defined as the ratio of the primary air supplied to the stoichiometric air required, calculated from the coal combusted. (iii) An investigation of the effect of temperature on sulphur retention with and without air staging. (iv) An assessment of the effect of fluidizing velocity on sulphur retention. EXPERIMENTAL SET UP Fluidized Bed Combustor and Ancillaries Figure 1 shows the main features of the fluidized bed combustor and ancillaries. The combustor was constructed from stainless steel and was 2.0m high and 0.3m square in section. The bed consisted of silica sand of mean size 0.665mm. The static bed height was 30cm. Fluidizing air, supplied by a fan, was metered and introduced through a distributor plate. When operating under staged condition, secondary air, supp 1 i ed by a compressor was metered and introduced into the combustor (usually the freeboard) through a stainless steel pipe. The secondary air injector (1.59Icm i.d., containing twelve 3.18mm holes) was located on the vertical central axis of the freeboard and allowed the secondary air to be injected in a horizontal plane 100cm above the bed surface. The geometry of secondary air injector rendered un i form d i st ri but i on of secondary air across a horizontal plane. (2 ) |
